Proposal: Provide the ability to monitor the usage of origins

webkit/browser/quota/usage_observer.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef WEBKIT_BROWSER_QUOTA_USAGE_OBSERVER_H_
+#define WEBKIT_BROWSER_QUOTA_USAGE_OBSERVER_H_
+
+#include "base/basic_types.h"
+#include "url/gurl.h"
+#include "webkit/browser/quota/quota_client.h"
+#include "webkit/browser/quota/quota_types.h"
+
+namespace quota {
+
+// This interface is implemented by subsystems that wish to monitor the storage
+// usage of origins. This is primarily used for origins that are granted
+// unlimited storage.
+class WEBKIT_STORAGE_BROWSER_EXPORT UsageObserver {
+ public:
+  struct WEBKIT_STORAGE_BROWSER_EXPORT Filter {
+    // The storage type to monitor. This must not be kStorageTypeUnknown.
+    StorageType storage_type;
+
+    // The quota client to monitor. This can be kAllClientsMask to monitor the
+    // aggregated usage for the given storage type and origin. In this case, the
+    // threshold will apply to the accumulated total usage.
+    QuotaClient::ID client_id;
+
+    // The origin to monitor usage for. Must be specified.
+    GURL origin;
+
+    Filter();
+  };
+
+  struct WEBKIT_STORAGE_BROWSER_EXPORT MonitorParams {
+    // Storage types and origin to monitor.
+    Filter filter;
+
+    // When the usage exceeds this threshold, the observer will be notified.
+    int64 threshold;

[tzik, 2014/03/17 05:31:56]

IMO, it's also desirable to get a notification on the usage goes below
|threashold|.

+
+    // After usage has exceeded the threshold, the observer can receive further
+    // notifications when usage continues to increase. |increments| specifies
+    // when these further notifications should occur, or can be set to zero to
+    // disable them.
+    int64 increments;

[tzik, 2014/03/17 05:31:56]

Can we start without |increments| for simpler implementation?
I think updatable |threashold| or multiple |threashold| are enough.

+
+    MonitorParams();
+  };
+
+  struct WEBKIT_STORAGE_BROWSER_EXPORT Event {
+    // The storage types and origin monitored.
+    Filter filter;
+
+    // The threshold that triggered this notification. Can be some |increment|
+    // above |threshold|.
+    int64 threshold;
+
+    // The current usage corresponding to the filter.
+    int64 current_usage;
+
+    Event();
+  };
+
+  // Will be called when the usage exceeds a threshold set by the observer.
+  virtual void OnUsageThresholdExceeded(const Event& event) = 0;
+
+ protected:
+  virtual ~UsageObserver() {}
+};
+
+}  // namespace quota
+
+#endif  // WEBKIT_BROWSER_QUOTA_USAGE_OBSERVER_H_